Electromagnetic device



Feb 16, 1960 R. P. c. RAsMUsEN 2,925,538

ELECTROMAGNETIC DEVICE Filed D60. 3l, 1956 2 Shee 13s-Sheet 1 Feb. 16, 1960 Filed Dec. 5l, 1956 TOTA L ATUATOQ PULL,

A PPLI E D VOLTAGE R. P. C. RASMUSEN ELECTROMAGNETIC DEVICE 2 Sheets-Sheet 2 AQMATUIZE STROKE @Warn cgt/Www United States Patent 0 F ELECTROMAGNEHC DEVICE Reidar P. C. Rasmusen, Columbus, Ohio, assignor, by mesne assignments, to Cutler-Hammer, Inc., Mila waukee, Wis., a corporation of Delaware Application DecemberSl, 1956, Serial No. 631,694

4 Claims. (Cl. 317-123) This invention relates to improvements in electromagnetic devices.

While not limited thereto, the invention is especially applicable to alternating currentcontactors and relays employed in electrical control systems of aircraft and the like where good quality of performance and low noise are required.

Various expedients have been proposed to eliminate undesirable variations in magnetic attraction in alternating current contactors due to the cyclic variation of an alternating current characteristic to maintain stability of an armature position throughout such variations. Because of the lack of uniformity of pull caused by cyclic variations of voltage, an undesired or false response of the contactor may occur. This is especially true where a high degree of sensitivity is required or where the contactor is subject to shock in its usual operation. Also the lack of uniformity in attraction of the armature due to the cyclic Variation of the current or voltage results in objectionable hum or noise and undesirable wear of the parts.

Among other things, it has been proposed to operate direct current contactors from an alternating current source through rectiers. Operating temperatures of these contactors at the high speeds and altitudes attained by aircraft have become so high that use of selenium and other common types of rectiliers to operate direct current contactors is becoming increasingly impractical. Use of rectiiiers to operate direct current contactors not only increases the cost but also adds several additional componentsto the contactor with a corresponding increase in the chance of failure.

:lt has also been proposed to employ a shading coil in inductive' relation to the energizing coil to afford a phase displacement of the alternating current induced in the former relative to that of the latter. It should be apparent that such phase displacement affords a resultant attractive flux having an absolute value that is main` tained above zero value at all times throughout the cyclic variations of the alternating current. However, the power consumed by a shading coil is directly proportional to the frequency of the alternating current applied to the energizing coil. Therefore, although a shading coil type device can be economically operated at the lower frequencies, the power consumption becomes so large at the higher frequencies such as 400 cycles used in aircraft systems as to render a shading coil impractical. Another disadvantage of a shading coil type device resides in its inability to afford a full 90 degree phase displacement between the two fluxes. The inductive reactance and resistance of a shading Acoil limit the phase displacement to i approximately 70 de rees and, therefore, the pull is not constant.

yIt has also been proposed to employ a pair of energizing coils, one of the coils being energized directly from an alternating current supply source and the other coil having a phase-shifting capacitorand a resistor in series connection therewith and the supply source to obtain a "ice phase displacement therebetween. When two coils are used, the optimum phase displacement of the magnetic uxes is degrees, although a small variation therefrom is not unsatisfactory. While this arrangement affords a substantially constant total pull on the armature, the center of application of the force on the armature will shift from one point to another corresponding to the axes of the respective coils at double the supply frequency.

In alternating current contactors operating at higher frequencies the problems attendant on non-uniformity of pull, noise, power consumption and undesirable vwear become especially pronounced. Although the power consumption of a shading coil type device remains within acceptable limits at the lower frequencies and up to approximately cycles where it equals that of a capacitor type device, at frequencies above 180 cycles and up to approximately 1,000 cycles the latter type is preferred. Since inrush of current is a function of frequency, the volt-amperes at an open condition of the armature might be so great as to affect the stability of the supply source at frequencies above 1,000 cycles. Additionally, noise of a given amplitude which may be tolerable to a human ear at the lower frequencies becomes o-bjectionable at higher frequencies.

Therefore, it is desirable to provide an eicient alternating current electromagnetic device having a long operational life and minimum components to reduce the possibility of failure. A uniform total attractive force having a fixed center of application on the armature is desirable to prevent the cyclic variations of the current or voltage from materially affecting the stability of the armature position. It is also desirable to reduce the hum and noise to a minimum and to afford greater pull on the armature without a corresponding increase in its size vand cost.

Accordingly, an object of the invention is to provide improved means affording the aforementioned and other functions.

A more specific object of the invention is to provide an improved alternating current electromagnetic device wherein stability of armature position is attained through uniformity of total attractive force having a `fixed center of application to the armature.

A still more specific object of the invention is to provide improved means for attaining the aforementioned uniform total attractive force and a xed center of application thereof to the armature throughout cyclic variations of the alternating current simply and economically without extraneous elements such as shading coils, rectiers and the like. n

A further specific object of the invention is to provide such electromagnetic4 device with improved means affording an approximately 90 degree phase displacement between the magneticfluxes developed by pairs of energizing coils.

Another specific object of the invention is to provide an improved alternating current electromagnetic device economically operable in the range of approximately 180 to 1,000 cycles having a plurality of force components symmetrically applied to the armature. Y

Other objects and advantages of the invention will hereinafter appear.

vice disclosed, inasmuch as itis susceptible of various modifications Awithout departing from the scope of the appended claims.

`In the accompanying drawings: Figure l is a view in perspective of an electromagnetic Patented Feb. 16, 1960 VFig. 4 illustrates.diagrammatically anY energizing circuit j for the device shown inrFig. l;

Fig. 5 graphicallydepicts pull characteristics for the device of Figs. l and14; and- Y Fig. 6 graphically depicts ux saturation characteristics e for the device shown in'. Figs. l and 4.

Referring to Figs. l, 2 and 3 an electromagnetic device embodying the invention is designated generally as 10. The device 10 has a four-legged stationary frame portion or core 1land'a movable armature V12 shown spaced from the core. Core- 11 has an intermediate portion or yoke 1.3 land four parallel poleV pieces or legsll, 16 and I7 formed integrally vwith the' yoke perpendicularly along the length of the latter. Yoke 13 is substantially larger in cross section at its mid-portion 18V between pole pieces 15 and 1621s shown in Fig. 3l, to accommodate the magnetic fluxes of both the inner and outer pairs of pole pieces. Surrounding the respective pole Vpieces are four preformed multiple turn operating coils 14a, 15a., lea and 17a for introducing magnetic fields 'in' the air gaps be-V tween the pole pieces and'armature 12'. Core-11 is constructed of a plurality of thin llat laminations 19 of suit'- able magnetic material such as Armco TO oriented iron or the like separated' from` one another by thin layers or coatings of insulating' material (not shown) which may bey previously applied to the laminationV stock material. The primary purpose oflaminating the core isY to reduce eddy current losses caused by the alternating magnetic ux. The laminated core is heldrtogether by being impregnated withV suitable adhesive to bond the laminations together'. The core and'rcoil assembly'ispottedin thermosetting resin Ztl in anopen end suporting enclosure 2l of non-magnetic materialsucl'r as stainlessV steel or the like' so that the free ends of the pole pieces extend through and slightly above' theopen end of the enclosure to facilitate grinding the sealing surfaces of the pole pieces. En-

closure 21 is provided with franges 22 and 23 on opposite side thereof, each flange having one or more holesV 22a and' 2311 therethrough to facilitateV securing the supporting enclosure to a stationary baise. A suitable number of holes 2.4 are providedV on one side wall of the enclosure to accommodate terminals 25 shown in Fig. Zito which the coil windings are connected.

Armature l2 is similarly constructed of a plurality of I thin llat laminations 26 of magnetic material such as f Armco, TO oriented iron or the like separated from one another by thin layers or coatings ofl insulating material (not shown) which may be previously applied to theV Y l laminations stock material. The laminated Varmature is held together by beingimpregnated with a suitable adhesive to bond the laminations together, wrapped with a plurality of layers 27 of glass tapeV and potted in a block 28 of thermo-setting resin; One side of' block 2S isopen to expose the sealing surface of the armature while the other" side has embedded in the resin a nut 2e and plate 30 rigidly secured tooneranother or other suitable means for attaching armaturen to a'driven element'for actuating contacts and the like. Armature 12 is normally biased away from the pole pieces by suitable'means (not shown) to provide air gaps therebetween.

An electrical circuit for energizing the electromagnetic device ofFigs. l, Zand 3 is shownin Fig. 4. The energiz-` ing circuit comprises conductorsLl. and LZ'connectable tliroughsuit'ableswitches to anQalternating' current power suply'source (not: shown); Operating coils la and 17a whichsurroundtheouter'polepieces14 and 17, respectively,v of core y11 areseries connected directly' acrossv Vpower supply conductors Ll, and L2 while operating coilsv 15a and 16a which surroundtiie inner'pole pieces 15 and 2,925,538 Y Y f* -16, respectively, of core 11 are series connected with a phase relative to the phase ofthe power supply source.

Coils 15a and 16a being in series connection with capacitor 31 and resistor 32 are energized in a phase displaced' relative to the phase of coils 14a and ln. Upon the energization of the two pairs of coils, armature r2 is attracted into contact with the pole pieces and remains in contact therewith so long as the coils' remain energized. When the coils are deenergiaed, armature l2 is released to return to its normally open position by force of the aforementioned biasing means. The primary function of capacitor 31 is to shift the phase of the alternatingcurrent flowing through coils 15a and loa relative to the phase of the current in coils 14a and 17a so that the magnetic fluxes developedv by the respective pairs of coils have a phase displacement of approximately 9G degrees. As a result, the total: attractive ilux has an absolute value which is maintainedabove zerovalue at all times throughout the cyclic variations of the alternating current. Since coils lSz and 16a which are energized in one phase surf round the inner pair of pole pieces while coils loa" and 17a which are energized inra different phase surround the' outer pair of' pole pieces and each pair of pole pieces ijs symmetrically arranged with respect to the center of the device, the magnetic forces developed thereby will always have a fixedcentralrpoint of application to the armature.'

This results in anelectromagnetic device, having a lotv.

level of noise an'd minimum wear.

The aforementioned phase relationship is obtained by providing capacitor 31 with a value of capacitanceV such that theA capacitive reactance is approximately equal to' the inductive reactance of coils lSa and ida to ehectap` proximate series resonance in the circuit. p An essential feature of Vthey invention is the provision of an arrange ment that will alford use of a capacitor 31 having a small value. Coils 15a and 16a have twice the number of turns requiredV to provide equal voltages across the inner' and outer pairs ofV coils. Thus, the voltage across coils ida v and 16a is twice the voltage across coils 14a andk fa.

Since the inductance varies as the square ofthe number of turns, the inductance of coils 15a and 16a would be 1 four times as great with twice the aforementioned number" of turns. Therefore, to have approximate series resonance in the circuitthe value of capacitance needbe only one-fourth as large. Since the number'of turns has been doubled, one half the currentrisV required to provide the samenurnber of ampere turns in the phase shifted inner-VV coils. T-his necessitates a' larger value of total series resistance to effect the current reduction. Since power loss',

varies as the square ofthe current and only 'as` the first power of the resistance, the series resistance consumes less power inthe novel arrangement.

`Fig. 5, wherein successive values'of Varmature pull are plotted against' lengthsof air gap or armature stroke to` cally depicts the'loadV characteristics.- Although the aforementioned curvesA, B and C'depict approximate values of armature pull throughout the armature stroke, it should be noted that not only at percent normal coil'voltage' .but also at' 65 percent normal coil voltage, the' novel device affords sufhcient pull to overcome the'opposiag' force'offthe load. Y.

Fig. 6; wherein successive values of applied voltage;

are'plott'ed'fa'gainstV values Vof vexcitingcurrent,` graphically-r e depicts llux' saturation characteristics ofthenove'l elec? trornagnetic device. Curve E shows the ux saturation characteristics for the pair of inner phase-shifted coils while curve F shows the ux saturation characteristics for the pair of outer line coils. An examination of these curves reveals that while the inductance of the outof-phase coils could change substantially when the core is driven to saturation as shown by the upper portion of curve E, the device has a wide range of operation in the substantially linear portions of the curves.

I claim:

1. In an electromagnetic device, a magnetic core having a plurality of spaced pole pieces, an energizing coil surrounding each of said pole pieces, a movable armature in cooperative relation with said pole pieces, an alternating current supply source, means comprising capacitor means in circuit with one pair of said coils for connecting said source to energize pairs of said coils with out-ofphase alternating currents to maintain the absolute value of the total attractive ux above zero value throughout the cyclic variations ofthe alternating current, and means integral with said one pair of coils for decreasing the value of capacitance required to provide resonance in said circuit.

2. The combination according to claim 1 wherein the last mentioned means comprises a number of turns in said one pair of coils alfording a voltage thereacross having approximately double the value of the voltage across another pair of said coils.

3. In an electromagnetic device, a magnetic core having a plurality of spaced pole pieces, a coil surrounding each of said pole pieces, an armature in cooperative relation with said pole pieces, and means for supplying pairs of said coils with substantially 90 degrees out-of-phase alternating currents comprising phase shifting means in circuit with one of said pairs of coils to maintain the absolute value of the total attractive flux above zero value throughout the cyclic variations of the alternating currents, said phase shifting means comprising a capacitor and resistance means in circuit with said one pair of coils, said capacitor having a value affording approximate resonance in the circuit.

4. In an electromagnetic device, a magnetic core having a plurality of spaced pole pieces, a coil surrounding each of said pole pieces, an armature in cooperative relation with said pole pieces, and means for supplying pairs of said coils with substantially degrees out-of-phase alternating currents comprising phase shifting means in circuit with one of said pairs of coils to maintain the absolute value of the total attractive flux above zero value throughout the cyclic variations of the alternating currents, said phase shifting means comprising a capacitor and resistance means in series connection with said one pair of coils, said capacitor having a value aording approximate series resonance in the circuit.

References Cited in the tile of this patent UNITED STATES PATENTS 779,432 Lindquist Jan. 10, 1905 2,591,520 De Fligue Apr. 1, 1952 2,775,742 Brogue Dec. 25, 1956 FOREIGN PATENTS 11,614 Great Britain May 10, 1910 943,740 France Mar. 16, 1949 OTHER REFERENCES Resonant Electrical Control Systems, Electrical Engineering, October 1943, pages 436-439. 

